The invention relates to the field of industrial inspection. More specifically, it relates to the inspection of the quality and integrity of junctions and connections, such as those for devices mounted on Printed Circuit Boards (PCBs).
It is known that an object such as a populated Printed Circuit Board Assembly (PCBA) may be inspected for defects by a procedure wherein such a PCBA is heated in order to obtain an infrared (IR) image via an IR camera. The captured image is then compared to a standard IR image of a known defect-free populated PCBA in order to evaluate the quality of the connections and junctions on the tested PCBA. What varies in the state of the art is the way the object under inspection is heated.
For example, U.S. Pat. No. 5,052,816 discloses a method and apparatus for junction inspection of electronic parts wherein a plurality of lead wires such as those from an IC (an integrated circuit) are irradiated by a fan beam at the same time. U.S. Pat. No. 5,208,528 discloses a method for inspecting a PCBA, and particularly for inspecting solder joints on the PCBA. This method is characterized by the heating of the PCBA, which is done either by pulsed or brief heating, or in a laminar fashion using a quartz lamp. U.S. Pat. No. 5,246,291 teaches a bond inspection technique for a semiconductor chip wherein a bonding process heats each package lead bonded to each contact area, and an IR camera captures an IR image. A laser can also be used to heat the leads, heating a plurality of leads at once. U.S. Pat. No. 5,984,522 discloses an apparatus for inspecting bump junctions in a semiconductor flip chip mounting wherein the surface of the semiconductor bare chip is irradiated with a laser light and radiation heat from the heated chip is detected with an IR camera.
Since it is essential to detect defects of electronic components such as Ball Grid Arrays (BGAs), Flip Chips, and semi-conductor devices, there is a need to provide an inspection technology, which is relatively easy to use, reliable, and can selectively identify defects due to absence, poor quality or out of tolerance of a solder joint.